Although cystic fibrosis (CF) is the most common, life-threatening autosomal recessive genetic disorder of the white population, there are often delays in diagnosis and hence start of treatment. Advances of the past two decades have made CF screening feasible using routinely collected neonatal blood specimens and measuring an enzyme level followed by CF mutation DNA analysis. Our overall goal of the study is to see if early diagnosis of CF through neonatal screening will be medically beneficial without major risks. ''Medically beneficial'' refers to better nutrition and/or pulmonary status, whereas '' risks'' include laboratory errors, miscommunication or misunderstanding, and adverse psychosocial consequences. Specific aims include assessment of the benefits, risks, costs, quality of life, and cognitive function associated with CF neonatal screening and a better understanding of the epidemiology of CF.